Field of the Invention
The present disclosure relates to a toner, a toner stored unit, an image forming apparatus, and an image forming method.
Description of the Related Art
Toners hitherto used for image formation, such as electrophotography, have been toners, where inorganic particles are externally added to toner base particles, in order to secure transferring properties within image forming apparatuses and chargeability.
However, inorganic particles externally added to toner base particles are embedded into the toner base particles by stress with a conveying member during conveyance of the toner inside a developing device. As a result, flowability of the toner is impaired, and toner supply properties, developing properties, and charging ability are deteriorated over time. Moreover, reduction in image density occurs when the toner is repeatedly used over a long period.
If the external additives are detached from the toner during developing, moreover, not only low image density and clogging of the developer are easily caused by reduction in chargeability and flowability of the toner, but also the toner is deposited and adhered onto a developing roller, an amount of scoped toner onto the area of the developing roller where the toner is adhered is reduced to cause formation of defective images.
If an amount of the external additives detached from the toner is large when the toner is transferred onto a photoconductor or an intermediate transfer belt, furthermore, filming of the external additive occurs on an entire area of the photoconductor or the intermediate transfer belt. As a result, optical properties and electric properties of the area of the photoconductor or the intermediate transfer belt where the external additives are filmed deteriorate and formation of defective images tends to be caused. An image forming apparatus typically include a cleaning system configured to remove filmed substances accumulated on a photoconductor or an intermediate transfer belt. However, a cleaning performance lowers particularly in a low-temperature and low-humidity environment, and problems tend to occur.
Meanwhile, it is difficult to completely prevent detachment of the external additives from the toner during image formation. If an appropriate amount of the external additives is supplied onto a photoconductor or an intermediate transfer belt, moreover, the supplied external additives help cleaning of the surface of the photoconductor or intermediate transfer belt. Therefore, such supply of the external additives is preferable.
In recent years, various methods have studies for producing a toner that granulated in a liquid, such as polymerization toners produced by suspension polymerization, emulsion polymerization or dispersion polymerization, in order to achieve small particle diameters and spherical shapes of toner particles. Particularly, toners having small particle sizes have a large total surface of toner base particles relatively. Therefore, it is necessary to increase an amount of external additives added in order to secure flowability of the toner. As the amount of the external additives increases, detachment of the external additives from the toner base particles tends to occur, leading to a problem that filming of the external additives increases. Accordingly, there is a need for a toner, which does not cause detachment of external additives until the toner is supplied into a developing device, and releases an appropriate amount of the external additives when the toner is transferred onto a photoconductor or an intermediate transfer belt.
As described above, a consideration of a way external additives are released from a toner is extremely important for continuously forming high-quality images. As a method for determining an easiness of external additive detaching from a toner, for example, disclosed is a wet method where vibrations are applied to a toner dispersion liquid by ultrasonic waves, and a ratio of the external additives detached from the toner is determined from a change in a weight of the toner after removing the external additives detached from the toner (see, for example, Japanese Patent No. 3129074 and Japanese Unexamined Patent Application Publication No. 2014-174341).